As a heat-shrinkable film, particularly a heat-shrinkable film for a label on a bottle body part, films including polyvinyl chloride, polystyrene, or the like are mainly used. However, with respect to polyvinyl chloride, in these years, chlorine gas generation at the time of incineration for disposal becomes a problem and with respect to polystyrene, there is a problem that printing is difficult, and heat-shrinkable polyester films almost free from these problems have drawn attention. However, regarding the conventional heat-shrinkable polyester film, since almost no drawing is carried out in the longitudinal direction orthogonal to the main shrinkage direction, in the case where it is shrunk and coated on a PET bottle or the like as a label, there is a defect that a label cannot be torn well along perforations (in other words, poor perforation-tear property). Further, a polyester film has a specific gravity of about 1.4 and there is a problem that the film is difficult to be separated from a bottle by gravity separation in water when the film is used as a label.
Therefore, a void-containing heat-shrinkage polyester film has been investigated in order to improve perforation-tear property of the heat-shrinkage polyester film and also to adjust the apparent specific gravity of the heat-shrinkage polyester film to lower than 1.00. A method in which an incompatible thermoplastic resin is mixed in the main raw material of the heat-shrinkage polyester film is proposed (Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Publication No. 2002-363312